Distortionless dynamic transmitter



' P. THOMAS DISTORTIONLESS DYNAMIC TRANSMITTER Filed April 18, 1922 WITNESSES:

INVENTOR 7 V I ATTORNEY cuit connections therefor, whereb 'Patented Aug. 14, 1928.

UNITED STATES PATENT OFFICE.

PHILLIPS THOMAS, OF EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

DISTORTIONLESS DYNAMIC TRANSMITTER.

My invention relates to telephone systems and apparatus and particularly to improvements in telephone receivers or transmltters of the moving coil type.

The principal object of my inventionas to provide a dynamic transmitter and cirthe motional curve of the transmitter iaphragm may be translated into corresponding potential variations without distortion.

In the ordinary type of telephone circuit, including a moving diaphragm and a cooperating coil, if harmonics are present in the diaphragm motion they do not have the same relative amplitude in the alternatingvoltage wave of the telephone coils. as in the diaphragm motional wave, inasmuch as the voltage generated in the telephone;co1ls is proportional, not only to the amplitude of vibration of the diaphragm, which is desired, but also to the frequency of the vibration.

According to my invention, I provide a telephone circuit which causes the wave form of the diaphragm vibration to be faithfully translated into corresponding potential variations without distortion, all as will be explained more full hereinafter.

With these and 0t er objects in view, my invention further consists in the mode of operation and details of construction hereinafter described and claimed and illustrated in the accompanying drawing wherein:

The single figure 1s a view, partially struc-- tural and partially diagrammatic, of a distortionless dynamic transmitter embodying my invention.

In the single figure is shown a well-known form ofdynamic transmitter comprising a magnetizable member 1 of E-shape having a pair of magnetic circuits as indicated by arrows 2 and 3, which include air-gaps 2a and 3a, respectively. The magnetic circuits may be energized by means of an exciting winding 4, which is wound upon a portion 5 of the magnetizable member 1 common to both magnetic circuits, from a direct-current source of energy 6 through an adjustable resistor 7. I

A transmitter diaphragm 8 of well known form is supported upon'suitable supporting members 9 and 11 which are mounted on the open end of the magnetizable member 1. "A coil 12 is wound upon a cylinder 13 which is connected to a mid point 14 of the diaphragm 8 by means of a member 15 and is so disposed as to lie in the air-gaps of both. magnetic circuits. It will be observed that by such disposition of the coil 12, movement thereof incident to vibration of the diaphragm 8 causes the generation of electromotive forces proportional to the product of the amplitude and the frequency of the vibration. K

According to my invention, the external circuit 16, which extends from opposite terminals of the coil 12 includes, in addition, an inductive reactance device 17 and a noninductive resistor 18. The inductance of the inductive reactance device 17 is so high that its impedance for the lowest frequency in the circuit 16 does not differ sensibly from the total impedance of the circuit.

The potential drop across the resistor 18, which results from the passage of currents in the circuit 16 generated by the motion of the coil 12, may be amplified by means of a well known type of thermionic tube 19, having a grid 21 and a hot cathode 22, which are connected to opposite terminals of the resistor 18 by conductors 23 and 24, respectively.

A plate-filament circuit for the tube 19 includes a source of direct-current energy 27 and a coupling coil '31. An outgoin or work circuit 32 is operatively connected to the coupling coil 31 through a coupling coil 33.

In operation, when the transmitter diaphragm 8 is set into vibration by sound waves, the coil 12 is correspondingly vibrated, thereby causing electromotlve forces to be generated in said coil. It will be observed, however, that if harmonics are present in the motional curve of the diaphragm 8, with the inductive reactance of the circuit 16 low in comparison to the total impedance thereof, the resulting electromotive forces and currents are distorted in value. One cause of the distortion is the fact that the voltages generated in the coil '12 are not directlyproportioned to the aming the circuit 16 are directly proportional to the amplitude of vibration of the diaphragm 8, and are independent of the frequency thereof. This is due to the fact that, while the voltage generated in the coil 12 is proportional to the frequency of vlbration of the diaphragm 8, so is the reactance of the inductance device 17 and, inasmuch as the currents traversing the circuit 16 are the quotient of the voltage by the impedance thereof, the currents will be independent of the frequency of vibration of the diaphragm 8. The modulated currents traversing the circuit 16 during vibration of the diaphragm 8 may be translated into correspondingly modulated potentials by means of the resistor 18. Hence, it can be seen that the motional curve of the diaphragm 8 may be translated into correspondingly modulated potentials without any of the distorting effects heretofore observed for the harmonics contained in the sound-wave form.

The potential drop across the resistor 18 may be amplified to any desired extent b means of three-electrode tube cascade amplification, using as the first tube of the series one in which the grid-filament resistance is large in comparison to that of the resistor 18. In order to simplify my invention, I have shown only one stage of amplification.

While I have shown only one embodiment of my invention, for the purpose of describing the same and illustrating the principles and operation thereof, it is apparent that various changes and modifications in the nature, the mode of o eration and the details of construction may e made without departing from the spirit of my invention. I desire, therefore, that only such limitations shall be imposed thereon as are indicated in the appended claims or demanded by the prior art.

I claim as my invention:

1. In an electrical system, a resilient member adapted to vibrate in accordance with the varying intensity of sound waves, means co-operatin therewith for translating the resulting fiindamental and harmonic frequency vibrations into modulated electromotive forces and a circuit includin said source of electromotive forces, a trans ating device and an inductance device, the ohmic resistance of said circuit being negligibl small as compared with the reactive im ed ance thereof, whereby the amplitude of the resultant modulated electromotive forces are caused to vary in accordance with the amplitude of said vibrations only.

2. In an electrical system, a resilient member adapted to vibrate in accordance with the varying intensity of sound waves, a coil adapted to be correspondingly vibrated b said member, means for producing a uniform magnetic field in the lane of said coil, said coil being so disposed as to vibrate in said uniform magnetic field only, whereby electromotive forces may be produced therein modulated in accordance with said vibration, a circuit, means for causing the amphtude of the currents in said circuit to var in accordance with the amplitude of said vi rations only and a resistor having low resistance value, said coil, means, and resistor being in series in said circuit, and means utilizing the potential across said resistor.

3. In an electrical system, a resilient diaphragm member adapted to vibrate in accordance with the varying intensity of sound Waves, a coil adapted to be correspondingly vibrated by said member, means for producing a magnetic field in the plane of said coil, said coil being so disposed as to vibrate in said magnetic field, whereby electromotive forces may be produced in said coil modulated in accordance with said vibration, a circuit including said coil, an inductive reactance device of such value as to substantially constitute the total impedance of said circuit for currents of the lowest frequency that may be contained therein and a resistor and a thermionic tube having input terminals, the latter being shunted around said resistor.

4. In a telephone system, the combination of a mechanically vibrating diaphragm, an electrical circuit, means for translating energy between said diaphragm and said circuit, the translated energy being depend ent upon the frequency, as well as the amplitude, of the vibrations to be translated, and means for causing the impedance of the circuit to vary with the frequency in such manner that the current variations are substan-' tially unaffected by frequency variations.

5. In a telephone system, the combination of a vibratory diaphragm, an electrical circult, a translating device responsive to a periodic electrical dimension of the energy 7 in said circuit, means operatively associating said circuit with said diaphragm in such manner that a different periodic electrical dimension of the energy in said circuit and the amplitude of vibration of said diaphragm do not have the same ratio under all conditions of vibration, and means for causing the impedance of said circuit to vary with the frequency in such manner that the first-named periodic electrical dimension has a substantially constant ratio to the amplitude of vibration of said diaphragm.

6. In a telephone system, the combination of a vibratory diaphragm, an inductance coil, means for causing a substantial correspondence between the composite alternating electromotive forces of said coil and the product of. frequency and amplitude of corresponding composite vibratory movements of sa1d diaphragm, a highly inductive circuit including said coil and having a negligibly small resistance as compared with the reactance thereof, and a translating device All termediate periodic electric energy proportional to the frequency as well responsive to the alternating current in said circuit.

7 The method of translating sound waves into periodic electric energy without distortion which comprises converting the sound waves into mechanical vibrations, producing from said mechanical vibrations an intermediate periodic electric energy. eipendent upon the frequency as well as the amplitude of said mechanical vibrations, and producing from said intermediate periodic electric energy electric energy dependent upon the amplitude of said intermediate electric energy and upon the frequency thereof, said dependency upon the frequency being opposite to the dependency of the intermediate periodic electric energy upon the frequency of the mechanical vibrations.

8. The method of translating sound waves into periodic electric energy without distortion which comprises converting the sound waves into mechanical vibrations, producing from said mechanical vibrations an indirectly as the amplitude of said mechanical vibrations, and producing from said intermediate periodic electric energy electric energy dependent upon the amplitude of said intermediate electric energy and inversely proportional to the frequency thereof.

9. In a telephone system, a mechanically vibratory diaphragm, an electro-dynamic generator, a translating device, means so actuating the electro dynamic generator ,from the diaphragm that the voltage delivered thereby is dependent upon the amplitude of the vibrations of said diaphragm and proportional to the frequency thereof, and transmitting means connecting said electro-dynamic generator to said translating device, said transmitting means including devices whereby the energy delivered to the translating device will be dependent on the amplitude of said voltage and inversely proportional to the frequency thereof, whereby the energy delivered to said translating device is not distorted by the efiects of the frequenc a 10-. In a sound-translating system, a device for delivering a voltage which changes upon change in the frequency of the sound, and a circuit upon which said voltage is impressed, said circuit including a reactive element and a. non-reactive element in series, said elements being so proportioned that the change in impedance of the reactive element with the frequency will counteract said change of voltage, whereby the voltage across one of said elements will be unaffected by changes in the frequency.

In testimony whereof, I have hereunto subscribed'my name this 17th day of April,

PHILLIPS THOMAS. 

